The fire arson investigator job specialty is created to provide the necessary expertise in the determination of the causes of arson fires and explosions and the criminal investigation of them.  The police fire arson investigator maintains a close liaison and working relationship with the fire department arson investigator, with police evidence technicians and other county, state and federal arson investigation units.  The police fire arson investigator is under the functional authority of the Investigative Section Commander, but is under the direction of the incident supervisor at a field scene.